Without limiting the scope of the present invention, its background will be described with reference to producing fluid from a subterranean formation, as an example.
After drilling each of the sections of a subterranean wellbore, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within each section of the wellbore. This casing string is used to increase the integrity of the wellbore by preventing the wall of the hole from caving in. In addition, the casing string prevents movement of fluids from one formation to another formation.
Conventionally, each section of the casing string is cemented within the wellbore before the next section of the wellbore is drilled. Accordingly, each subsequent section of the wellbore must have a diameter that is less than the previous section. For example, a first section of the wellbore may receive a conductor casing string having a 20-inch diameter. The next several sections of the wellbore may receive intermediate casing strings having 16 -inch, 13⅜-inch and 9⅝-inch diameters, respectively. The final sections of the wellbore may receive production casing strings having 7-inch and 4½-inch diameters, respectively.
Each of the casing strings may be hung from a casinghead near the surface. The casinghead or spool is a heavy, flanged steel fitting connected to the first string of casing that provides a housing for slips and packing assemblies, allows suspension of intermediate and production strings of casing, and supplies the means for the annulus to be sealed off. Typically, a casing hanger provides the frictional gripping arrangement of slips and packing rings used to suspend casing from a casinghead in the well. Alternatively, some of the casing strings may be in the form of liner strings that extend from the setting depth up into another string of casing. Liners are typically suspended from the upper string by a hanger device such as a liner hanger that provides an arrangement of slips and packing rings.
It has been found, however, that each of these conventional casing techniques require multiple tubulars of decreasing diameters. Accordingly, production resources are not optimized and production is limited by the diameter of the smallest tubular. Moreover, the wellbore must be drilled to accommodate the larger tubulars and other downhole equipment such as blow-out preventers (BOPs) must be of an appropriate size to accommodate the larger tubulars.
Therefore a need has arisen for a system and method for casing a wellbore that optimizes resources while maintaining hydraulic and mechanical stability. A need has also arisen for such a system and method that minimizes the number of sizes of casing required to case the wellbore. In addition, a need has arisen for a system and method for casing a wellbore that minimizes the size requirements of equipment near the surface.